Silicone rubber has been bonded to a variety of substrates using various primer compositions. For example, U.S. Pat. No. 3,498,824 to Chadha discloses a process for bonding silicone rubber to a substrate using a primer composition containing an organic solvent and mono- and di-hydrocarbonoxy substituted acyloxysilanes. U.S. Pat. No. 2,979,420 to Harper discloses a process for bonding room temperature vulcanizable silicone rubber to a variety of substrates using a primer composition containing monohydrocarbon triacyloxysilanes and partial hydrolyzates thereof. The patentee further discloses that hydrocarbonoxy silanes of the formula R.sub.n Si(OR').sub.4-n have been found to be inoperative as a primer for bonding room temperature silicone rubber to a variety of materials.
Also, U.S. Pat. No. 3,377,309 to Harper describes a method for bonding room temperature vulcanizable silicone rubber to a variety of substrates which comprises coating a substrate surface with a composition containing a phenyl-containing siloxane resin, an alkylsilicate, a chlorosilane and the balance being a non-halogenated solvent; drying the coated substrate and thereafter applying a room temperature vulcanizable silicone rubber to the dried substrate.
Most of the processes employed heretofore for bonding curable silicone rubber to a substrate utilize compositions containing organic solvents. These organic solvents are generally considered to be hazardous in the workplace as well as to the employees. In addition, the costs of monitoring the environment and removing the solvent are substantial. Also, primer compositions which contain organic solvents are generally highly flammable and are to be avoided, if possible. Therefore, the use of aqueous primers which are substantially free of highly inflammable and hazardous organic solvents is desirable.
Water soluble silane compositions have been described in U.S. Pat. No. 2,965,515 to Jellinek for treating fibrous glass material to make laminated products from resins and glass cloth. These water soluble silane compositions consist of vinylalkoxysilanes of the formula EQU RSi[(OC.sub.2 H.sub.4).sub.n OR'].sub.3
where R is vinyl, R' is a methyl or ethyl hydrocarbon radical and n is at least one and not greater than about 7.
Surprisingly, applicants have found that heat curable silicone rubber can be bonded to a variety of substrates using a primer composition containing an aqueous solution of an alkenyltrihydrocarbonoxysilane containing an organic solvent which is miscible with water. This is totally unexpected in view of the teachings of U.S. Pat. No. 2,979,420 to Harper which teaches that hydrocarbonoxy silanes are inoperative as primers for bonding room temperature vulcanizable silicone rubber to a variety of substrates.
It is, therefore an object of this invention to provide a process for bonding heat curable silicone rubber to a variety of substrates. Another object of this invention is to provide a process for bonding heat curable silicone rubber to a variety of substrates using an aqueous primer composition. Still another object of the present invention is to provide an aqueous primer composition for bonding heat curable silicone rubber to a variety of substrates. A further object of the present invention is to provide an aqueous primer composition which is stable after long-term storage.